Answer:
Please check explanation.
Step-by-step explanation:
It looks like that your iPhone crashes at the time of startup.
It might be you are not following the right steps to sneak peek into the recovery mode.
You need to connect the charger cable to your iPhone and your computer, ( Lightning mode in USB).
You need to hold your home button and then wake/sleep button for only few seconds.
As the screen is turned off, you need to release the wake/sleep button however, hold the home button meanwhile, and the screen is most likely going to remain off during this time.
Now you need look for the iTunes on your computer just to ensure it detects the phone is in the right mode(recovery).
Now you need to use the iTunes to restore the software.
If you are not being helped this way, it might then be like you have disturbed your logic board. And there can be various reasons for this, and most probably you are not using the correct ESD protection while you were repairing. You will find in the guide that you might experience the shock; however, this is not correct, the ESD damage can lead to the shocks that you cannot experience.